In March of 2021, SNS accounts for 'Trainee A' were opened and gradually six pre-debut trainees were unveiled, consisting of Inhyuk, Jihoon, Leo, James, Sangwon and a hidden member. A number of executives and producers followed their SNS accounts, sparking rumors from fans that the trainees will be the next new boy group to debut under BigHit Music. Due to the large attention they have gained online, Trainee A has quickly amassed several thousands of followers across their social media accounts in less than two months.
On August 2, it was revealed that Junil had left the group.
On August 22, the "About" section from the group's YouTube's channel was updated and JJ was revealed as the hidden member.